Cast Vs. Pressed Pumps
Despite their description - pumps are not all made equally. What can be described as a stainless-steel pump can mean something very different when manufactured. Metal pumps can be made in one of two ways – by pressed or cast metal. Both deliver very differing product features.
What is Pressed Pump Construction?
Pressed pumps are typically made from sheet metal cut to shape and formed to the desired shape. The metal is usually only a few mm thick and can be deformed with relative ease if a blow or knock is delivered to the casing. Pressed pumps are typically designed for simple applications using clean fluids which do not contain solids. Such pumps are usually similar in design by being closed coupled and directly driven by a motor.
The construction of pressed pumps is usually used in conjunction with plastics, cast iron and rubber parts for submersible pumps to enable the pump to be more rugged and durable. In end-suction pumps the complete casing is made in stainless steel, however, outlet fittings are usually welded to the casing. This can cause a couple of issues such as the weld can leak due to weld perforation and connections are not usually designed to withstand high pressures.
What is a Cast Pump?
Cast pumps are manufactured quite differently and are ruggedly designed. Pumps are manufactured using molten metal formed into shapes via lost foam or sand casting within moulds. The casings are then machined according to designed tolerances. Due to the method of casting, castings are made thick to allow for differences during casting. As castings are thick they ensure many years of trouble-free service. Some models are designed to be long coupled and are able to accommodate a variety of mechanical seal designs ensuring suitability for a wide variety of process fluids thus extending their application across a wide variety of industries.
Cast pumps are designed to accommodate wear rings which not only improve pump efficiency but wear in place of the casing. The wear rings are placed either side of the impeller and are then replaced as the pump wears prolonging pump casing life and maintaining efficiency.
Cast pumps are robust enough to accommodate large solids passing through as due to the density of the metal the casing will not deform should solids pass through the pump. Impellers are also dense enough to handle knocks and will not be misshaped.
Castings can be manufactured in a variety of different blends to accommodate fluid requirements from stainless steel, to 316L, aluminium bronze or just bronze meaning a pump can be created for your specific fluid requirement or design life. Pressed pumps are usually manufactured from either 304 or 316 stainless steel limiting their application.
Although the outlay may be more initially, cast pumps are a better investment for longevity given that their design often incorporates many features such as mechanical seal options, long-coupled pumps for process use and the ability to replace wearing parts such as wear rings to improve working life. Components within cast pumps are more likely to be sourced from OEMS as they are branded and pressed pumps are usually built with the suppliers own seal, motor and bearings making replacement only available through distributors.